Default isolation level

[mrn]

What is the default isolation level set for a
transaction in a database? Is it read commited or serializable ?

--
| Mike Nixon
| Unix Admin
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http://www.instantflashshop.com

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[karluk]

It's read committed, according to this excerpt from the Oracle 8i concepts manual.

"Oracle offers the read committed and serializable isolation levels, as well as a read-only mode that is not part of SQL92. Read committed is the default and was the only automatic isolation level provided before Oracle Release 7.3."

 

[Guest_imported]

As Karluk says it's Readcommitted.........unless you are running the query through Microsoft Transaction Server - then it's Serializable.

 

[sunpatil]

can somebody tell me what is readcommited and serailizable.

please explain the concept.

thanx in advance.

regards

sunpatil

 

[karluk]

Both read committed and serializable disallow "dirty reads", so that when you select from a table you don't see anyone else's uncommitted transactions.

Serializable offers additional features that make transactions seem to happen in a specific order, even though in reality they are in progress simultaneously. Serializable offers "repeatable read", which ensures that if you select the same rows a second time in your transaction you will not see updates that were committed after your first select. Similarly you are guaranteed that a second select won't return new rows that weren't in your first select.

The serializable isolation level offers nice features, but comes at a cost of higher overhead. That's probably why Oracle chose read committed as its default. It's up to the programmer to design a transaction and know whether to increase the isolation level to serializable.

 

[sem]

Besides nice features serializable level brings some limitations: you can not update rows, changed by others during your transaction.

 

[sunpatil]

THANX CARLUK AND SEM.

REGARDS

SUNPATIL